Classifications

• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
  • C12P19/00—Preparation of compounds containing saccharide radicals
  • C12P19/04—Polysaccharides, i.e. compounds containing more than five saccharide radicals attached to each other by glycosidic bonds
  • C12P19/06—Xanthan, i.e. Xanthomonas-type heteropolysaccharides
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S435/00—Chemistry: molecular biology and microbiology
  • Y10S435/8215—Microorganisms
  • Y10S435/911—Microorganisms using fungi

Definitions

• the present invention concerns an improvement to the injectivity and to the filtrability of xanthan gums in oil formations in view of improving the recovery of crude oil; it concerns more particularly a suitable treatment making use of a particular type of enzymatic system, to obtain limpid solutions of these xanthan gums whose injectivity and flowing properties through the oil formations do not result in a loss of intrinsic properties of the polysaccharide and particularly of its thickening power.
• Xanthan gums are hydrophilic polysaccharides obtained by fermentation of suitable nutrients based on carbon hydrates, under the action of certain microorganisms, particularly bacteria of the Xanthomonas genus. Xanthan gum has numerous applications both in the food domain and in the petroleum domain. An important application consists of using xanthan gums for displacing oil from partially depleted crude oil reservoirs.
• the xanthan gums constitute a particularly useful thickening agent.
• they are characterized by a high insensitivity to salinity and to the nature of the salts, in particular, they do not precipitate and their viscosity does not decrease in the normal conditions of use and also, they exhibit a high stability to mechanical stresses.
• the xanthan gums also suffer defects, the more important of which consists of quickly clogging the oil formation in the immediate vicinity of the injection well, and thus preventing any flushing of this formation and, accordingly, any additional oil extraction or recovery.
• the raw fermentation broths as well as the xanthan gums precipitated and separated from the fermentation broths contain a certain number of insoluble particles issued from the fermentation step, such as bacteria cells or other cell fragments, which are difficulty separated from the fermentation juice or from aqueous dispersions of xanthan gums, essentially as a result of the very high viscosities thereof.
• the xanthan gum aqueous solutions freed from the materials insoluble therein by means of various known techniques such as filtration at high pressure gradients through calibrated filters or through beds of diatomaceous earth, are also clogging at a relatively small distance from the injection well, where the pressure gradients become negligible and the flowing velocities are very low.
• the xanthan gum aqueous solutions still contain even after having removed the insoluble particles (clarification treatment), a certain number of translucent aggregates, deformable under the effect of the high stresses prevailing at the inlet of the formation at the vicinity of the injection well and which, over all, are not removable by mere filtration or centrifugation of these aqueous solutions.
• the presence of these aggregates, also called microgels seems to be favored by inadequate conditions of isolation and precipitation of the powdered polysaccharide from the fermentation juice.
• One way of conducting the injectivity test consists of measuring, versus time, the accumulated volume of filtrate of the polysaccharide solution passing through a calibrated filter of a diameter of 47 mm or still of 142 mm and whose pore size ranges from 0.45 to 5.0 ⁇ m under a constant manometric pressure from 10 kPa to 300 kPa, thus simulating both the pore sizes of the formation around the injection well and the high pressure drops encountered therein.
• the detection of the microgels present in the aqueous solution of xanthan gum may be effected by means of the so-called flowing or filtrability test as described in the article of N. KOHLER and G. CHAUVETEAU "Xanthan polysaccharide plugging behavior in porous media-Preferential use of fermentation broth" Journal of Petroleum Technology, February 1981, pages 349 to 358.
• This test is characterized by the injection at constant rate, by means of a double-action pump, of a clarified solution of xantan gum, through one or more calibrated filters of a pore diameter higher than 0.8 ⁇ m, for example filters with a pore diameter of 3 ⁇ m.
• This injection is preferably effected at rates corresponding to those encountered on the field, inside the formation typically lower than one meter per day.
• a differential pressure sensor With the help of a differential pressure sensor, the pressure drops on both sides of the filter are recorded versus time for polymer solution and comparatively with the aqueous phase used for solubilizing the latter: ⁇ P polymer/ ⁇ P water.
• This ratio of the pressure drop of the polymer solution as compared to that of water when circulated through the same porous medium (filters or natural porous media) is also called mobility reduction R ⁇ .
• Another characteristic magnitude which is usefully controlled during such flowing of polymer solutions through porous media consists of the relative viscosity ⁇ , ratio of the viscosity of the polymer solution to that of the dissolving water, whose value must not vary or only vary to a small extent during such flowing experiments.
• a correct evaluation of the penetration and flowing capacity of a polysaccharide solution inside a petroleum formation must be made by means of one of the two above-mentioned tests, i.e. an injectivity test providing for the evaluation of clogging at the inlet of the formation by insoluble particles as well as a flowing or a filtrability test at constant flow rate for evaluating the clogging, if any, due to microgels at a certain distance from the injection well.
• test conditions constitute a compromise between the injectivity test under high pressure, for checking the absence or presence of residual insoluble particles of a size greater than 0.8 ⁇ m, and the flowing test, under a lower pressure, for estimating the amount of microgels remaining in solution.
• a perfectly purified xanthan gum solution will then be characterized by the substantially perfect linearity of the accumulated filtrate volumes versus time.
• the U.S. Pat. No. 3,729,460 proposes a technique for improving the limpidity and injectivity of xanthan gum raw solutions by means of a chemical treatment with an alkaline solution, preferably in a pH range from 11.2 to 12.8 under high temperature (up to 120° C.).
• an alkaline solution preferably in a pH range from 11.2 to 12.8 under high temperature (up to 120° C.).
• the use of strongly basic pH values is liable to lead to the conversion of the primary structure of the xanthan gum and to depolymerization. It has been established in article of D. LIPTON "improved Injectability of Biopolymer Solutions" preprint SPE No.
• the U.S. Pat. No. 4,010,071, No. 4,119,491, and No. 4,165,257 describe clarification processes for raw fermentation juices or aqueous solutions of xanthan gums with the use of an enzyme of the protease type.
• the treatment takes place preferably in a strongly basic medium (7.5 ⁇ pH ⁇ 13) and at temperatures lower than 60° C. A low salinity of the water and particularly a divalent ions content thereof lower than 100 ppm is recommended.
• the U.S. Pat. No. 4,094,739 proposes to clarify Xanthomonas fermentation broths whose microbial cells have been first deactivated by pasteurization: a second fermentation with the use of a microorganism of the fungus type, solubilizes, in the presence of additional glucose, the residual Xanthomonas cells initially difficulty filtrable in view of their small size, by producing insoluble cells of a much larger size, more easily filtrable.
• This treatment consequently requires a preliminary filtration of said cells and nothing indicates to which extent the injectivity and filtrability of the obtained solutions are improved.
• the U.S. Pat. No. 4,182,860 describes a clarification process consisting of solubilizing xanthan gum in a brine containing a minimum of 0.5% by weight of salt, followed with heating, at a temperature of at least 100° C., and with a further filtration, whereby is obtained a limpid solution.
• This process has the double disadvantage of requiring two steps, the filtration before the injection into the formation being indispensable, and of also resulting in a non-negligible risk of degradation of the xanthan gum as the result of the use, over a long time, of a high temperature and, consequently, in a loss of its thickening properties.
• a first object of this invention is to provide a new method for clarification of aqueous solutions of xanthan gums, wherein the thickening power of these gums is maintained. Another object of this invention is to provide a method for clarification of the raw fermentation juice. Another object of the invention consists in the removal of the insoluble cell fragments produced in the fermentation process of these xanthan gums. Another object of the invention consists of improving the injectivity of xanthan gum solutions for their use in enhanced oil recovery. Still another object of the invention consists in the removal of microgels and hence in the improvement of the flowing properties of the xanthan gum solutions inside an oil formation at a certain distance from the injection well. Finally, another object of the invention consists in the use of solid compositions whereby during their dissolution in water, the limpidity, injectivity and flowing properties of said xanthan gum solutions are improved. Other objects of the invention will be made apparent from the following description thereof.
• the enzymatic treatment of the invention is effected at a pH lower than 7, and, preferably, higher than 3, in aqueous medium having a concentration of dissolved salts of alkali and/or alkaline-earth metals of at least 10 -1 equivalent/liter.
• the temperature and the contact time are selected so as to be sufficient for obtaining the desired clarification without substantial viscosity decrease.
• the polysaccharases of Basidiomycetes have a glucane hydrolase activity and, more specifically, a ⁇ -1,4-glucane glucanohydrolase or ⁇ -1,4-glucanase activity (E. T. REESE and M. MANDELS, Canadian Journal of Microbiology vol. 5, 1959, pages 173-185 and, particularly page 177). Accordingly, they are able to hydrolyze the main chain of the xanthan gum, known to be constituted of ⁇ -1,4-D-glucose recurrent units.
• Basidiomycete polysaccharases which constitute typical exo-enzymes (D. R. Barras and coll., above cited, page 116) provide for an improvement of the filtrability and injectivity of the xanthan gum solutions.
• One of the advantages of the invention is that it is not necessary to purify the enzyme, the raw preparations being perfectly convenient.
• the xanthan gums subjected to the treatment of the invention are, preferably, inactive gums, i.e. gums which have been subjected to a deactivation treatment of the Xanthomonas cells or other biologically active agents present in the culture medium at the end of the fermentation step, said treatment having for object to stabilize the xanthan gums and to protect them against subsequent biological attacks.
• This treatment well known in the art, consists for example in a sterilization, pasteurization, acidification or chemical treatment, for example by means of formaldehyde, ethylene oxide, propylene oxide, ⁇ -propiolactone, glutaraldehyde or pivololactone and analogs.
• the proportion of xanthan gum is, for example, from 0.01 to 3% and preferably from 0.04 to 1.5% by weight, with respect to water, and the enzyme proportion is, for example, from 0.001 to 0.5% by weight, preferably from 0.0025 to 0.05% by weight with respect to water, these proportions being not limitative.
• the minimum enzyme amount to be used is obviously dependent on the amount of active factor present in the selected preparation.
• the treatment by polysaccharase may be directly effected on the deactivated raw fermentation broth; in this case the enzyme is directly admixed with the raw fermentation broth or diluted with injected water, preferably containing from 0.04 to 1.5% by weight of xanthan gum, the mixture being then subjected to incubation.
• the obtained product may then be dissolved again, irrespective of the pH value, the temperature and the ionic strength of the dissolving water.
• the Basidiomycete polysaccharase not only degrades the cell fragments and solid bacteria suspended in the xanthan gum solutions by converting them to hydrosoluble compounds, so as to finally obtain a limpid solution of xanthan gum, but also, and this is more surprising, the transluscent microgels responsible for the clogging of the oil formations at a certain distance from the injection well. In all of these operations of clarification and microgels removal, the thickening power of the xanthan gums is maintained.
• the treatment by polysaccharases leads to limpid solutions of xanthan gum and to the improvement of both the injectivity and the flowing properties of said solutions, as shown by the corresponding tests through calibrated filters.
• the Basidiomycete polysaccharase develops its maximum activity in a medium of acid pH, lower than 7 and higher than 3, advantageously a pH from 3 to 6.
• a medium of acid pH lower than 7 and higher than 3, advantageously a pH from 3 to 6.
• an acid for example hydrochloric acid, acetic acid or sulfuric acid.
• the enzymatic treatment according to the invention takes place during an incubation period of, for example, from 0.5 to 60 hours, and preferably from 3 to 15 hours, at temperatures ranging from room temperature (25° C.) up to about 65° C., preferably from 40° to 60° C.
• Short treatment times are preferably associated with high temperatures and conversely.
• the optimum time will be short, for example 4 hours at 50° C., 1 or 2 hours at 60° C.
• the preferred temperatures range from 30° to 50° C. but must not however exceed the temperature beyond which the polysaccharase enzyme is liable to deactivate to a noticeable extent.
• the aqueous solution containing the xanthan gum and polysaccharase is preferably stirred smoothly, continuously or periodically.
• Another original feature of the invention is that the treatment by means of polysaccharase gives satisfactory results only when it is effected in the presence of water containing a sufficient concentration of dissolved salts. This minimum amount decreases with the temperature of the enzymatic treatment and it is accordingly difficult to give a very precise value thereof. It is at least 10 -1 equivalent/liter and, in some cases at least 1 equivalent/liter.
• the salts which are involved in the salinity calculation are mainly soluble salts of alkali or alkaline-earth metals.
• the minimum of 10 -1 equivalent/liter corresponds to 10 -1 mole of NaCl or 0.5 ⁇ 10 -1 mole of CaCl 2 or of Na 2 SO 4 .
• xanthan gum in solution may have two different conformations in accordance with the total salinity and temperature of the solution: disordered conformation in distilled water or in water of low salinity (lower, for example, than 10 -1 equivalents/liter for a temperature from about 25° to 40° C.), well-ordered conformation at higher salinities (higher than about 10 -1 equivalent/liter in a temperature range which may extend much beyond the deactivation temperature of the enzyme).
• This conformational transition in accordance with the salinity and the temperature may be followed, for example, by measuring the rotary power [ ⁇ ] or, alternatively the reduced viscosity.
• the polysaccharase must be used in conditions of temperature and ionic strength such that the well-ordered structure is stable.
• An approximate value of the minimum salinity at each temperature and, conversely, of the maximum temperature for each salinity, can be obtained from the following empirical formula:
• An empirical formula similar to the above one may also be deduced for divalent ions as well as for mixtures or monovalent ions with divalent ions. For the diluted polymer solutions at concentrations lower than 1 g/l, the polymer concentration will be omitted in the calculation.
• the amount of dissolved salts required for carrying out the invention naturally exists in most of the oil-field waters and the clarification treatment by polysaccharase may thus be directly performed on the oil field by means of the oil-field water, without it being necessary to adjust the salinity.
• it is desired to proceed to the enzymatic treatment directly with the fermentation broth for example at the outlet of the fermenter, this does not pose problems either since the fermentation broth contains a certain amount of nutritive salts necessary for the fermentation, the total salt content, which is variable according to the fermentation process, being usually higher than the minimum above-stated concentration.
• the treatment with polysaccharase is not greatly affected by the nature of the salts and in particular, the presence of divalent ions such as calcium and magnesium ions, imparting to water a certain hardness, is perfectly tolerated and has no indesirable effect on the enzymatic clarification process.
• solid compositions containing xanthan gum and Basidiomycete enzyme may be directly added to the oil-field water, removing thereby any requirement of separate addition of enzyme to the xanthan gum solution.
• These solid compositions have a particular interest when the enzymatic clarification must be achieved, for example, in situ, during an enhanced recovery operation. The enzymatic reaction will progress with the solubilization of the polysaccharide and, if the temperature is conveniently selected, the enzymatic clarification process will not extend the usual time required for the preparation of the injected xanthan gum solution.
• This solid composition may contain, for example, from 1 to 100 and, preferably form 2 to 30 parts by weight of xanthan gum per part by weight of enzyme.
• This exo-enzyme is allowed to act for 48 hours at 50° C., the pH is then brought back to 7 and the obtained limpid solution is diluted to a concentration of 400 mg/l of polymer by means of water containing 20 g/l of NaCl.
• the untreated raw broth results in a substantial clogging of the inlet filter, essentially due to the presence of insoluble particles in suspension, and a low and progressive clogging of the following filters which may be attributed to the effect of the microgels.
• a viscosity decrease ( ⁇ is also observed during the passage of the untreated raw broth through the filters, this being not the case with using the broth treated with enzymes.
• Aqueous dispersions of powdered polysaccharide Rhodopol 23 R, batch No. 79-123-1, of RHONE-POULENC INDUSTRIES COMPANY have been made in waters of different salt contents, at a concentration of 1600 mg/l.
• 500 mg/l of the enzyme of example 1 is added and the treatment is performed at a temperature of 43° C. for variable times (Table 3).
• the enzymatic treatment according to the invention consequently provides for an improvement of the filtrability of the xanthan gums in a powdered form.
• This example is destined to show the advantage of using enzymes of the Basidiomycete type as compared with other enzymatic preparations, consisting either of polysaccharases or proteases (P).
• dispersions at 1600 mg/l of a powdered saccharide Rhodopol 23 R, batch No. 80-269, of RHONE-POULENC INDUSTRIES Company have been prepared in water containing 20 g/l of NaCl and treated with 500 ppm of various enzymatic preparations, at a pH corresponding to the maximum of activity.
• Table 4 summarizes, for each enzymatic preparation, the treatment conditions, as well as the accumulated volumes of filtrate through a Millipore filter of 0.8 ⁇ m under 10 kPa, obtained after 35 minutes of filtration.
• the activity of the polysaccharases according to the invention is about 10 times that of the other polysaccharases or of proteases.
• the polysaccharases of Aspergillus niger and Trichoderma reesei which are known to have a ⁇ 1.4 glucane exo-hydrolaser activity, do not provide for an improvement of the filtrability of xanthan gum as powder in water of selected salinity as is the case with Basidiomycete exo-enzymes.
• These Aspergillus niger and Trichoderma reesei polysaccharases have no significant effect on the microgels of the polymer in spite of the fact that the water salinity is higher than 10 -1 M/l.
• This example is destined to show the specific action of the polysaccharases according to the present invention on the microgels contained in a xanthan gum in powder form.
• a xanthan gum in powder form For this purpose there was first prepared a 400 mg/l dispersion of Xanflood xanthan gum powder, batch No. 14 630 of Kelco Company, U.S.A., in water containing 20 g/l of NaCl and 400 mg/l of NaN 3 .
• This solution was then clarified by filtration according to a standard method (Millipore filters of 3 ⁇ m and then 0.8 ⁇ m under 100 kPa) in order to remove the insoluble particles and make it limpid.
• the zanthan gum contained in the fermentation broth of example 1 and which has been subjected to the treatment with the polysaccharase of the same example, is precipitated with 50% ethyl alcohol.
• the precipitate is then washed with pure isopropyl alcohol, then dried under vacuum for 2 days in a vacuum drier at 50° C.
• This example is destined to determine how accurately, for a given temperature of the enzymatic treatment (38° C.), the salinity limits for which the viscosity of the xanthan gum is not affected or, likewise, the salinity limit for a given temperature at which the xanthan gum is in well-ordered conformation.
• Two solid compositions each containig 1.6 g of xanthan gum Rhodopol 23 R, batch No. 80-269, RHONE-POULENC INDUSTRIES, FRANCE, 500 mg of polysaccharase obtained from Basidiomycete Poria and 400 mg of NaN 3 , are first prepared.
• Each of these solid compositions is dispersed in one liter of water at pH 5 containing 20 g of NaCl.
• the enzymatic treatment is effected while varying only the temperature and the treatment time: A: 12 hours at 43° C., B: 30 hours at 30° C.
• a reference solution C which contais 1.6 g/l of xanthan gum and 0.4 g/l of NaN 3 is also prepared.

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• 1980
  • 1980-10-06 FR FR8021395A patent/FR2491494B1/fr not_active Expired
• 1981
  • 1981-09-26 DZ DZ816321A patent/DZ324A1/fr active
  • 1981-10-02 DE DE19813139249 patent/DE3139249A1/de active Granted
  • 1981-10-03 IN IN1110/CAL/81A patent/IN156553B/en unknown
  • 1981-10-05 GB GB8130007A patent/GB2085904B/en not_active Expired
  • 1981-10-05 RO RO105464A patent/RO83405B/ro unknown
  • 1981-10-05 BR BR8106391A patent/BR8106391A/pt not_active IP Right Cessation
  • 1981-10-06 CA CA000387407A patent/CA1172588A/fr not_active Expired
  • 1981-10-06 JP JP56160058A patent/JPS5791194A/ja active Granted
  • 1981-10-06 MX MX819698U patent/MX7182E/es unknown
  • 1981-10-06 US US06/309,147 patent/US4416990A/en not_active Expired - Lifetime

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